What is this?

[Firefish89]

Hi,

Any ideas? It came with a coral shipment.

 

[Firefish89]

It does not roll into a ball, so maybe not Sphaeromatidae. An online image search suggests Paracerceis sculpta (https://en.wikipedia.org/wiki/Paracerceis_sculpta). Which seems to have a cool life cycle, if that is what it is.

 

[ISpeakForTheSeas]

That is a male Sphaeromatid isopod (the giveaway in your pics is the elongated uropods by the telson; i.e. the long prongs by the tail):

Haha, yeah that's a male Sphaeromatid isopod - the long "prongs" by the tail (the elongated uropods) are a good way to tell, same with the conglobation (rolling into a ball); the eyes can be a good tell, but some Cirolanids and similar have small eyes as well, so it's not my preferred method of differentiating them. Another way is by looking at the underside of the tail - flat = bad; round (domed/vaulted) = good.

Also, Paracerceis sculpta is a kind of Sphaeromatid isopod (I don't know if that's the species you have or not, but yours should be a keeper regardless). Definitely an interesting life cycle there!